The use of photosensing systems in industry and other areas to detect the presence or absence of objects has become prevalent in recent years. Photosensing systems include one or more photoelectric transmitters for projecting a beam of light (preferably a beam of modulated light) and one or more associated photoelectric receivers. Photoelectric transmitter and receiver pairs are packaged either together in the same housing or in separate, spaced-apart housings. When a transmitter/receiver pair are packaged in the same housing, a diffuse, specular or retroreflective surface is used to redirect the source light from the transmitter back to the receiver. When the transmitter/receiver pair are spaced-apart, the source light usually impinges directly on the receiver without being redirected after it leaves the transmitter. Spaced-apart transmitter/receiver pairs are commonly referred to in industry, and hereinafter, as thru-beam photosensors. Regardless of the nature of the transmitter/receiver pair, a change in the detection of the light beam creates control signal information that is used to control or communicate with various types of equipment. The change may be the interruption of a transmitter light beam caused by a passing object or the sensing of a transmitter light beam that is normally blocked by the presence of an object. As will be readily appreciated by those skilled in the photosensing art, these are only representative examples of the many uses to which photosensing systems are put.
As will be understood from the foregoing description, one of the requirements of a photosensing system is that the photoelectric transmitter and the photoelectric receiver be aligned such that the light beam produced by the transmitter impinges upon the light sensitive surface of the photoelectric receiver. In the past, thru-beam photosensors have been aligned using the visual feedback created by an indicator light emitting diode (LED) located on the back, top or front of the receiver housing.
When the receiver mounting is adjusted to align the receiver's field of view with the transmitter's light beam, the back and top located indicators are readily visible to the installer or person maintaining the photosensing system. Contrariwise, front located indicators are generally difficult or impossible to see.
When the transmitter mounting is adjusted to align the transmitter's light beam with the receiver's field of view, prior art indicators located on the top and front of the receiver housing are generally visible at separation distances of up to 25 feet. Beyond this distance these indicators cannot be seen. Prior art indicators located on the back of the receiver housing are not visible from the transmitter location. While prior art top and front mounted receiver indicators are not bright enough to be seen at distances greater than about 20 feet, prior art thru-beam photosensors are capable of operating at much larger separation distances (up to 1000'). The reason why top and front mounted receiver indicators are viewable only up to about 20 feet is due to the fact that, in the past, such indicators have been designed to provide wide viewing near the sensor. Thus, while prior receiver indicator designs are suitable for aligning thru-beam sensors in short-range detection environments, they do not satisfy alignment needs in long-range detection environments. In this regard, it should be noted that, frequently, the housings of thru-beam photosensors are commonly one and the same with diffuse proximity and retroreflective housings within a product "familie." This is done to reduce manufacturing costs and to maintain a common aesthetic image.
As a result, in the past, the alignment of long-range, thru-beam photosensors has been cumbersome and expensive when such sensors are used in applications such as remote perimeter security systems and spanning large tanks and conveyors. Methods currently in use include: the temporary connection of an external bright lamp to the sensor output; locating one employee at the transmitter and another at the receiver that work together to align the system; and, having one employee walk back and forth between the transmitter and receiver.
As will be readily appreciated from the foregoing discussion, there is a need to provide a simpler, more efficient way to align the transmitter and receiver of a long-range, thru-beam photosensor system. The present invention is directed to providing a visible alignment indicator designed to simplify the alignment of thru-beam photoelectric transmitter and receiver pairs.